System and method for calibrating and determining hearing status

ABSTRACT

Method and System for characterizing an incident pressure wave in a hearing test. The method includes introducing a sound signal of a predetermined frequency and amplitude into an ear canal, measuring at least a sound pressure level (Pm) in the ear canal, processing information associated with the sound pressure level, obtaining at least an acoustic reflectance (R) based on information associated with the sound pressure level, and determining an incident wave pressure parameter (P+) in the ear canal according to the following formula: P + = P m 1 + R .

1. CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional No. 60/894,432,filed Mar. 12, 2007, incorporated by reference herein for all purposes.

2. BACKGROUND

The present invention relates generally to hearing screening anddiagnostic techniques. More specifically, the invention provides amethod and system for calibrating hearing equipments and determininghearing status. Merely by way of example, the invention has been appliedto audiometer, but it would be recognized that the invention has a muchbroader range of applicability.

Hearing loss can be categorized by where or what part of the auditorysystem is damaged. There are three basic types of hearing loss:conductive hearing loss, sensorineural hearing loss and mixed hearingloss.

Conductive hearing loss occurs when sound is not conducted efficientlythrough the outer ear canal to the eardrum and the tiny bones, orossicles, of the middle ear. Examples of conditions that may cause aconductive hearing loss include: conditions associated with middle earpathologies such as fluid in the middle ear from colds, allergies, pooreustachian tube function, perforated eardrum, benign tumorsdisarticulated ossicles, ossification of ligament, impacted earwax, andinfection in the ear canal.

Sensorineural hearing loss occurs when there is damage to the inner ear(cochlea) or to the nerve pathways from the inner ear (retrocochlear) tothe brain. Sensorineural hearing loss can be caused by diseases, birthinjury, drugs that are toxic to the auditory system, and geneticsyndromes. Sensorineural hearing loss may also occur as a result ofnoise exposure, viruses, head trauma, aging, and tumors.

Mixed hearing loss results when a conductive hearing loss occurs incombination with a sensorineural hearing loss. In other words, there maybe damage in the outer or middle ear and in the inner ear (cochlea) orauditory nerve.

Various techniques have been developed for screening hearing problem.For instance, an analysis of the acoustic power reflectance in the earcanal has been shown to be effective in diagnosing conductive hearingloss problems while an otoacoustic emission test (OAE) has been shown tobe effective for diagnosing sensorineural hearing loss issues.

Acoustic power reflectance is the measurement of the amount of powerbeing reflected from the ear drum, middle ear structure, and/or cochlea.More specifically, it is defined as the ratio of the forward-moving(incident) pressure wave to the reflected (retrograde) pressure wave.Consider an acoustic pressure wave that travels along an ear canal, aslong as no discontinuities exist in the ear canal, the acoustic powerthat is conveyed by the pressure wave propagates unimpeded to theeardrum. The eardrum then conducts the acoustic power into the middleear. However, due to mismatch in ear canal impedance, while some of theincident power that reaches the eardrum will enter the middle ear, theremainder is reflected back into the ear canal. The reflected powertakes the form of a retrograde pressure wave in the ear canal.

The magnitude and latency of the reflected waves as a function offrequency, is a useful indicator of the status of the middle ear.Reflected acoustic power that is significantly different in magnitude orlatency from that of a normal ear will likely reveal the precise natureof a disorder.

The otoacoustic emission test (OAE), on the other hand, measures thesounds that the ear produces in response to stimulation. There are twocommon types of otoacoustic emissions in clinical use: Transientotoacoustic emissions (TOAEs) or transient evoked otoacoustic emissions(TEOAEs) are sounds emitted in response to a train of acoustic stimuliof very short duration. These stimuli are usually clicks but can betone-bursts. Distortion product otoacoustic emissions (DPOAEs) aresounds emitted by the cochlear hair cells in response to twosimultaneous tones of different frequencies.

While the above mentioned hearing testing techniques are extensivelyused in the detection of hearing loss, the presence of standing wave canadversely affect calibration of audiometers and also the accuracy ofthese hearing tests. Therefore, it would be desirable to have hearingtest methods and systems that produce result that are affected byreduced distortions from standing waves or even free from any distortionby standing waves.

3. SUMMARY OF THE INVENTION

The present invention relates generally to hearing screening anddiagnostic techniques. More specifically, the invention provides amethod and system for calibrating hearing equipments and determininghearing status. Merely by way of example, the invention has been appliedto audiometer, but it would be recognized that the invention has a muchbroader range of applicability.

An embodiment of the present invention provides a method forcharacterizing an incident pressure wave in a hearing test. The methodincludes introducing a sound of a predetermined frequency and amplitudeinto an ear canal, measuring at least a sound pressure level (P_(m)) inthe ear canal, processing information associated with the sound pressurelevel, obtaining at least an acoustic reflectance (R) based oninformation associated with the sound pressure level, and determining anincident wave pressure parameter (P₊) in the ear canal according to thefollowing formula:

$P_{+} = {\frac{P_{m}}{1 + R}.}$

Another embodiment of the present invention provides a method fordetermining a hearing threshold by determining an incident wave pressureparameter and turning it into a power intensity parameter for use inconducting equipment calibrations and hearing loss measurements.

Another embodiment of the present invention provides a method fordetermining a hearing threshold. The method includes providing a probesuitable for placement in an ear canal, the probe being configured todeliver a tone associated with one or more frequencies and one or morevolume levels and further configured to measure one or more soundsignals, determining a threshold volume level for the tone, measuring atleast a sound pressure level of the ear canal at the threshold volumeusing the probe; processing information associated with the measuredsound pressure level, obtaining an acoustic reflectance based on atleast information associated with the measured sound pressure level,determining a threshold value for an incident wave pressure parameter inthe ear canal based on at least information associated with the measuredsound pressure level and the determined acoustic reflectance, whereinthe threshold value for the incident wave pressure parameterrepresenting the hearing threshold.

Another embodiment of the present invention provides a system fordetermining an incident wave pressure in a hearing test. The systemincludes a probe adapted to be placed in a ear canal, the probe includesa source transducer for delivering a sound and a receiving transducerfor detecting a sound, a signal generator connected to the sourcetransducer, the signal generator being configured to send one or morefirst electronic signals to the source transducer for delivering thesound, a signal processor connected to the receiving transducer, thesignal processor being configured to receive one or more secondelectronic signals from the receiving transducer and to determine atleast a sound pressure level (P_(m)) based on at least informationassociated with the one or more second electronic signals, a dataprocessor connected to the signal processor, the data processor beingconfigured to receive and process at least information associated withthe determined sound pressure level (P_(m)) and to determine an acousticreflectance (R), and wherein the data processor is further configured todetermine an incident wave pressure parameter (P₊) in the ear canalaccording to the following formula:

$P_{+} = {\frac{P_{m}}{1 + R}.}$

Another embodiment of the present invention provides a method forcharacterizing an incident pressure wave in a hearing test. The methodincludes introducing a sound of a predetermined frequency and amplitudeinto an ear canal, measuring at least a sound pressure level (P_(m)) inthe ear canal, processing information associated with the sound pressurelevel, obtaining at least an acoustic reflectance (R) based oninformation associated with the sound pressure level, terminating theear canal with its own characteristic impedance, and determining anincident wave pressure parameter (P₊) in the ear canal according to thefollowing formula:

$P_{+} = {\frac{P_{m}}{1 + R}.}$

The present invention has various advantages over conventionaltechniques. Certain embodiments can provide hearing testing systems andmethods that produces results that are affected by reduced influence ofstanding waves or even free from any influence by standing waves. Someembodiments can provide hearing testing systems and methods that couldbetter distinguish inner ear hearing problems from middle ear hearingproblems.

Some embodiments of the present invention can significantly lower thecost of ear screening. For instance, some embodiments of the presentinvention reduce the number of false-positives in a hearing testingprograms by distinguishing middle ear problems from inner ear problems.

Some embodiments of the present invention provide more accuratedetermination of hearing status by isolating the incident wave pressuremeasurement from that of measured pressure, thereby eliminating theeffects of standing waves. As a result, the power measurement is abetter representation of the actual sound power that is beingtransmitted to the inner ear.

Some embodiments of the present invention provide significantimprovement over conventional ear screening methods by taking intoaccount of the retrograde waves. For example, some embodiments of thepresent invention derive a power measurement that reduces the effect ofthe retrograde waves on the power measurement, thereby making themeasurement more accurate.

In some embodiments of the present invention, the incident wave pressurecan be used for better hearing aid fitting.

With a more accurate measurement of the incident power to the ear drum,some embodiments of the present invention allow for a more reliablecalibration of the audiometer.

With a more accurate measurement of the sound level delivered to theinner ear, some embodiments of the present invention allow for a moreaccurate result from the pure tone audiometry, distortion productotoacoustic emission measurements, transient otoacoustic emissionmeasurements, and stimulus frequency otoacoustic emission measurements.

Depending upon embodiment, one or more of these benefits may beachieved. These benefits and various additional objects, features andadvantages of the present invention can be fully appreciated withreference to the detailed description and accompanying drawings thatfollow.

4. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a simplified block diagram of a method for determining anincident wave pressure according to an embodiment of the presentinvention.

FIG. 2 shows two conventional sections of the basic transmission linemodel according to an embodiment of the present invention.

FIG. 3 is a simplified block diagram of a method for determining ahearing threshold according to an embodiment of the present invention.

FIG. 4 is a simplified diagram illustrating a system for determining anincident wave pressure according to an embodiment of the presentinvention.

5. DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to hearing screening anddiagnostic techniques. More specifically, the invention provides methodsand systems for calibrating hearing equipments and determining hearingstatus. Merely by way of example, the invention has been applied toaudiometer, but it would be recognized that the invention has a muchbroader range of applicability.

As described above, in conventional techniques, the presence of standingwaves can adversely affect the results of these hearing tests.Specifically, standing waves are nulls (or nodes) formed from thedestructive interaction between the incident and the reflected waves.These pressure nulls are developed at positions where the two waves areout of phase. If the stimulus frequency is such that one of thesepressure nulls is near the entrance to the emission probe, then themeasured pressure would be substantially attenuated. As a result, therecan be a discrepancy as large as 15-20 dB between the sound pressurelevel measured by the emission probe and the sound pressure level at theeardrum. In other words, because of the pressure cancellation effect ofthe standing wave, the sound pressure level recorded at the probe maynot accurately reflect the actual sound pressure at the eardrum.

The problem is further exacerbated if the patient suffers from mixedhearing loss. In such cases, the conductive hearing loss caused bypathologies in the middle ear will tends to further distort the actualincident power that is delivered to the inner ear. As a result, testresult may indicate that a patient suffers inner ear problem even whennone exists.

In other words, conventional techniques for calibration and hearing lossdetection are often inadequate due to the distortion of the measuringparameters by standing waves and middle ear pathologies. Morespecifically, conventional calibration techniques, such as ReferenceEquivalent Sound Pressure Level (RETSPL) defined in the ANSI S3.6 1996standard or ear canal pressure measurement, fail to compensate forstanding wave effect caused by the reflected wave. Recently, there hasbeen some discussion of a real-ear intensity calibration based on apaper entitled “Comparison between intensity and pressure as measures ofsound level in the ear canal” published in J. Acoust. Soc. Am. 104 in1998 by Neely S. T. and Gorga, M. P. However, the proposed intensitymeasurement is solely derived from the overall pressure measurement,which includes power contribution from both the forward and backwardwave components. While the use of this total power intensity forcalibration and measurement has mitigated some of the distortion problemcaused by standing waves, the measurements are still susceptible to afair amount of standing wave distortion. Therefore, one of the intentsof this invention is to propose a new method for calibration andmeasurement that uses an intensity value derived from the forwardcomponent of the measured wave pressure only, thereby avoiding theproblems associated with standing wave interference entirely.

FIG. 1 is a simplified block diagram of a method for determining anincident wave pressure according to an embodiment of the presentinvention. The diagram and the associated description are provided onlyas an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For instance, while themethod described below relates to pure tone audiometry (PTA) only, thedescribed method may easily be adapted for use with various other typesof hearing screening methods such as otoacoustic emission (OAE)measurements and auditory brainstem response (ABR) measurements.

The method 100 includes a process 102 for delivering a sonic stimulus toa ear canal, a process 104 for measuring the pressure generated (P_(m))in a ear canal, a process 106 for providing the power reflectance (R) ofthe ear canal, a process 108 for determining the incident wave pressure(P₊), a process 110 for determining the incident power intensity, and aprocess for performing equipment calibrations and hearing measurements.Although the above has been shown using a selected sequence ofprocesses, there can be many alternatives, modifications, andvariations. For example, some of the processes may be expanded and/orcombined. Other processes may be inserted to those noted above. Furtherdetail of the present invention can be found throughout the presentspecification and more particularly below.

At the process 102, a sonic stimulus is delivered to the ear canal usinga sound source transducer positioned at the opening of the ear canal.Depending on the application, the sonic stimulus may be a tone, a chirp,multiple tones, or other stimulus type. In one embodiment, the sonicstimulus can be a pure tone of a predetermined frequency and amplitude.In another embodiment, a pure tone frequency at 1 kHz may be chosen forthe hearing test. In yet another embodiment, the tone may be a wide bandsweep (chirp) of a range of frequencies within the human audible range.In yet another embodiment, two sound source transducers may be used togenerate two pure tones to stimulate a measurable distorted emissionfrom the cochlear hair cells. In yet another embodiment, the soundsource transducer is a speaker housed in a ear probe.

At the process 104, the pressure in the ear canal is recorded. In oneembodiment, the pressure is measured using a receiving transducerpositioned at the opening of the ear canal. In another embodiment, thereceiving transducer is a microphone embedded in the same ear probe thathouses the speaker.

At the process 106, the power reflectance (R) of the ear canal iscomputed. In one embodiment, the power reflectance may be derived fromthe measured pressure as it is disclosed in a paper by Susan E. Voss andJont B. Allen entitled “Measurement of Acoustic Impedance andReflectance in the Human Ear Canal.” 95 J. Acoust. Soc. Am. 372 (January1994). In another embodiment, the acoustic reflectance may be measuredusing one of a plurality of reflectance measurement systems, such as theMEPA3 Clinical Reflectance System, manufactured by Mimosa Acoustics,Inc.

At the process 108, the incident wave pressure (P₊) in the ear canal isextracted from the measured pressure (P_(m)). In one embodiment, theincident wave pressure (P₊) is a function of the measured ear canalpressure (P_(m)) and the ear canal reflectance (R) according to thefollowing equation:

${P_{+}(f)} = \frac{P_{m}\left( {x,f} \right)}{1 + {R\left( {x,f} \right)}}$

where x is the distance of the microphone from the ear canal and f isthe frequency of the selected sonic stimulus.

As shown in the equation above, while the measured pressure (P_(m)) andthe reflectance (R) are both functions of x and f, the ratio of P_(m) toR is a function of the f only. As a result, the incident wave powerintensity is independent of the probe location and thus free from anydistortion by standing waves. In order to calibrate an audiometer it isnecessary to remove the standing wave field from the measured pressure.Namely the pressure of interest is not the total pressure, rather it isthe incident pressure P₊. The voltage on the loudspeaker is thendetermined such that P₊(f) is constant with respect to frequency. Bydoing this, the intensity delivered to the cochlea will be constant,under the assumption that the intensity absorbed by the middle ear islossless.

At the process 110, once the incident wave pressure is computed, theincident power intensity (I₊), which is defined as power per unit area,may be derived from the following equation:

${I_{+} = \frac{{P_{+}}^{2}}{Z_{0}}},$

where Z₀ is the wave characteristic impedance that is defined by thefollowing equation:

${{Z_{0}\left( {x,s} \right)} = \frac{\rho_{0}c}{A(x)}},$

where ρ₀ is the density of air, c is the speed of sound, and A(x) is thearea of the ear canal.

Therefore, the incident power intensity (I₊) may be calculated from themeasured pressure (P_(m)) according to the following equation:

$I_{+} = {\frac{P_{m}^{2}}{{Z_{0}\left( {{1 + R}} \right)}^{2}}.}$

In one embodiment of the present invention, the ear canal is terminatedin the characteristic impedance of the ear canal (Z₀) to prevent theretrograde pressure (P−) from affecting incident wave intensity value.

At the process 112, the calculated P₊ or I₊ is used for performingcalibration of the audiometer or making hearing measurements. Forexample, a key concept behind certain embodiments of the presentinvention is that P+ is more highly correlated to the hearing thresholdthan the microphone pressure Pm, because the function 1+R(f) removes theeffect of standing waves. For another example, the calculated P₊ or I₊may be used for real-ear calibration of the audiometer. Because thecalculated P₊ and I₊ are free from the influence of standing waves andmiddle ear pathologies, and because they are independent of the positionof the probe in the ear canal (they do not depend on x), they provide amore accurate calibration for the audiometers. The calculated P₊ and I₊may also be used in a various OAE measurements such as distortionproduct otoacoustic emission measurement, transient otoacoustic emissionmeasurement, and stimulus frequency otoacoustic emission measurement.

Although the above has been shown using a selected sequence ofprocesses, there can be many alternatives, modifications, andvariations. For example, some of the processes, such as the processes102, 104, and 106, may be combined. In another example, a process, suchas the process 110, may be skipped.

In another embodiment, we know that the energy travels at the wave speedin the forward direction, is reflected by inhomogeneities and byspreading of the wave as it propagates, and then travels in the reversedirection. The product of the wave pressure (P) and wave velocity (U)determines the wave intensity. (Here, the wave velocity is adistinctively different entity from speed of sound. In the followingdiscussion, we shall use the term “velocity” or “U” to mean the acousticvelocity of the wave and the term “speed” or c to indicate the velocityof the wave front. As shown above, the wave impedance is given by

${Z_{0} = \frac{\rho_{0}c}{A}},$where c is the speed of sound. On the other hand, the wave power isgiven by P*U where P is the pressure and U is the wave velocity.) In thegeneral case the wave speed (c) can depend on frequency and position. Weexplore the relationships between the forward and backward travelingwave variables (pressure and volume velocity) [P₊(x,ω), U₊(x,ω)] and[P⁻(x, ω), U⁻(x, ω))] for inhomogeneous media, and then give formulasfor the forward and backward intensity flow, and its velocity, in termsof the medium's constitutive relations.

FIG. 2 shows two conventional sections of the basic transmission linemodel, as a lumped parameter electrical circuit. Inductance representsmass per unit length and while the capacitance represents stiffness perunit length, in such a representation for a section A meters long. Inthe following discussion, we shall denote p_(±)(x, t) as the wavepressure in the forward (anterograde) and reverse (retrograde)directions, and u_(±)(x, t) as the anterograde and retrograde wavevelocities. In some cases we shall let u represent the volume velocity.The Fourier and Laplace transforms are indicated by upper case letters.For example p₊(x, t)

P₊(x, ω). When subscripts are required, the ± will be indicated assuperscripts (e.g., P_(i) ⁺(x, ω)). The symbol

 indicates a transform pair.

A medium's wave properties are characterized by the per-unit lengthseries impedance

 (x, s) and the per-unit length shunt admittance Y (x, s), denoted hereas constitutive relations. In the ear canal the medium is air and

 is determined by the density of the air and Y by the air's stiffness.

Intensity has direction, collinear with that of the velocity. The totalpressure and particle velocity have corresponding forward and retrogradecomponents. It follows from wave linearity, that without loss ofgenerality, the pressure (a force per unit area) may be written as a sumof anterograde P⁺ and retrograde P⁻ propagated pressure waves as, forexample,P(x,ω)=P ⁺(x,ω)+P ⁻(x,ω).  (1)

Likewise, the axial velocity U (a flow) may be expressed as, forexample, a “sum” of anterograde and retrograde axial velocity travelingwave componentsU(x,ω)=U ⁺(x,ω)−U ⁻(x,ω).  (2)

The retrograde velocity component is negative because velocity, likeintensity, has direction, whereas pressure is a scalar, withoutdirection.

The ratio of the pressure and velocity for forward and backwardtraveling waves is equal to an inhomogeneous impedance we call thecharacteristic impedance, denoted ζ₀ (x, t) in the time domain and Z₀(x, s) in the frequency domain, such that

$\begin{matrix}{{\left. {\zeta_{0}\left( {x,t} \right)}\leftrightarrow{Z_{0}\left( {x,s} \right)} \right. = \frac{P_{\pm}\left( {x,\omega} \right)}{U_{\pm}\left( {x,\omega} \right)}},} & (3)\end{matrix}$

independent of the direction of the wave (as above). For homogeneouswaves Eq. 3 is well known.

The two inhomogeneous material properties

 (x, s) and Y (x, s) define the wave properties via two functions, thewave characteristic impedance, for example, can be defined as

$\begin{matrix}{{{Z_{0}\left( {x,s} \right)} \equiv \sqrt{\frac{\left( {x,s} \right)}{{??}\left( {x,s} \right)}}},} & (4)\end{matrix}$and the wave propagation functionγ(x,s)=√{square root over (

(x,s)y(x,s)×)}{square root over (

(x,s)y(x,s)×)}.  (5)

The wave characteristic impedance is important because it is used in thedefinition of wave intensity, while the wave propagation functiondetermines the speed of sound (c), as a function of position andfrequency.

Given Eq. 3 it follows that the average forward (+) and retrograde (−)intensity is, for example,

$\begin{matrix}{{{{{\overset{\_}{I}}_{\pm}\left( {x,\omega} \right)} \equiv {\frac{1}{2}\; P_{\pm}U_{\pm}^{*}}} = {{\frac{1}{2}\; Z_{0}{{U_{\pm}\left( {x,\omega} \right)}}^{2}} = {\frac{1}{2}\;{Y_{0}\left( {x,s} \right)}{{P_{\pm}\left( {x,\omega} \right)}}^{2}}}},} & (6)\end{matrix}$where Y₀=1/Z₀ and

 indicates the real part.

The pressure and velocity are related by the line impedance Z(x, s),defined as the pressure over the velocity

$\begin{matrix}{\left. {\zeta\left( {x,t} \right)}\leftrightarrow{{Z\left( {x,s} \right)} \equiv \frac{P\left( {x,\omega} \right)}{U\left( {x,\omega} \right)}} \right. = {\frac{P^{+} + P^{-}}{U^{+} - U^{-}} = {{Z_{0}\left( {x,s} \right)}{\frac{1 + {\left( {x,s} \right)}}{1 - {\left( {x,s} \right)}}.}}}} & (7)\end{matrix}$where we have used our previous definitions Eq. 1, Eq. 2 and Eq. 3. Inthe time domain p(x, t)=ζ(x, t)*u(x, t) at every point x on the line. InEq. 7 the reflectance R(x, s) is defined in the frequency domain as thetransfer function between incident and reflected waves at a location xalong the line, namely

$\begin{matrix}{{{R\left( {x,s} \right)} \equiv \frac{P_{-}\left( {x,\omega} \right)}{P_{+}\left( {x,\omega} \right)}} = {\frac{U_{-}\left( {x,\omega} \right)}{U_{+}\left( {x,\omega} \right)}.}} & (8)\end{matrix}$

The wave variables P±, U± are related to each other via the reflectance.From the above definition of the reflectance, and from Eq. 7, a littlealgebra gives, as an example,

$\begin{matrix}{{R\left( {x,s} \right)} = {\frac{{Z\left( {x,s} \right)} - {Z_{0}\left( {x,s} \right)}}{{Z\left( {x,s} \right)} + {Z_{0}\left( {x,s} \right)}}.}} & (9)\end{matrix}$

For example, in the time domain p⁻(x, t)=q(x, t)*p₊(x, t), where *represents the time convolution operator, namely

p⁻(x, t) = ∫_(τ = 0)^(∞)−q(x, τ)p₊(x, t − τ)𝕕τ.

A similar relation holds the velocity wave variables. Given Z(x, s) andZ₀(x, s), one may find the reflectance R(x, s) from Eq. 9.Alternatively, given R(x, s) one may find the normalized impedance Z(x,s)/Z₀(x, s). Physically this means that the reflectance ismathematically related to the impedance, normalized by Z₀. Thus thedefinition of the characteristic impedance for inhomogeneous anddispersive media plays a fundamental role in relating wave variables tointensity flow.

The wave equation for the pressure p(x, t) is, as an example,

$\begin{matrix}{\frac{\partial^{2}{p\left( {x,t} \right)}}{\partial x^{2}} = {\frac{1}{c^{2}}{\frac{\partial^{2}{p\left( {x,t} \right)}}{\partial t^{2}}.}}} & (10)\end{matrix}$

The general solution of the wave equation is, for example,p(x,t)=p ₊(t−x/c)+p ⁻(t+x/c),  (11)where p₊(ξ) and p⁻(ξ) are two arbitrary functions. This solution tellsus that the wave equation supports forward and backward propagated“waves,” which are represented in two arbitrary functions p₊ and p⁻,traveling at the speed of sound c (or if one considers theelectromagnetic case, of light), in the forward and backward directions.These two solutions (p₊ and p⁻) are denoted as wave variables, sincethey are of the form of forward and backward traveling pressure(voltage) or velocity (current) waves. Equation 11 indicates that anyfunction, having arguments t±x/c, is a solution of the wave equation.The incident wave is denoted the anterograde wave, while reverse(reflected) traveling wave is denoted the retrograde wave.

The units of the waves are indeterminate and open to choice. Foracoustic problems the waves may be pressure p or velocity u. Inelectrical problems it may be voltage, current, electric or magneticfield, scalar or vector, or even probability waves, as in quantummechanics. Note, for example, that by simple linear transformation, thesolution of a linear, time-invariant (i.e., LTI), dispersionless (c isindependent of frequency f) second-order differential equation (Eq. 10),may be written either in terms of (1) the sum of two pressure waves[p₊(x, ω),p⁻(x, ω)] (for the acoustic case), or (2) two velocity waves[u₊(x, ω), u⁻(x, ω)], or a combination of (3) pressure and velocity[p(x, ω), u(x, ω)]. In each case appropriate boundary conditions arerequired to provide the scaling of the two degrees of freedom providedby these various representations.

The wave variables in equation 11 are very physical as they describe thesolution of the wave equation in a natural manner, as waves going in thetwo directions. There is something special about each of these waves inthat they transport energy in the two directions, in an uncoupledmanner. The waves are uniquely specified in terms of the intensityproperty. The pressure is the sum of the forward and reverse pressure,and each wave pressure (or velocity) uniquely defines the intensity viathe characteristic impedance. Since the two intensity are independent(they depend only on the boundary conditions), the wave variables areuniquely specified for this case.

With reference to FIG. 2, the basic equation for dispersiveinhomogeneous media: an important and well known generalization of Eq.10 is the LTI, causal, dispersive, inhomogeneous pair of first orderequations

$\begin{matrix}{{\frac{\mathbb{d}}{\mathbb{d}x}\begin{bmatrix}{P\left( {x,w} \right)} \\{U\left( {x,w} \right)}\end{bmatrix}} = {- {{\begin{bmatrix}0 & {Z\left( {x,s} \right)} \\{y\left( {x,s} \right)} & 0\end{bmatrix}\begin{bmatrix}{P\left( {x,w} \right)} \\{U\left( {x,w} \right)}\end{bmatrix}}.}}} & (12)\end{matrix}$where P(x, ω)) is the pressure (or voltage), U(x, ω) is the velocity (orcurrent),

(x,s)=R(x,s)+sL(x,s),  (13)is the per unit length series impedance, andy(x,s)=G(x,s)+sG(x,s)  (14)is the per unit length shunt admittance, where by definition R and G arethe real part of

 and Y, and in a loss-less medium are zero.

One cannot determine the formula for the wave speed c in terms of

 and Y from Eq. 10 without an additional relationship. However given Eq.12, this relation may easily be determined, since

 and Y are explicitly specified in the formulation. Equation 12 iscalled the Webster Horn equation, (in acoustic applications), or theTelegraph equation (in electromagnetic applications). It follows thatEq. 12 is more general that Eq. 10, and represents a generalization inthe sense that it defines the waves directly in terms of the medium'sconstitutive relations

(x, s) and Y(x, s), in general can be location and frequency dependent.Equation 12 it is typically written as a single second-order equation.

The constitutive relations

(x, s) and Y(x, s) may be determined only by an experiment on a givenphysical system, or by a theoretical model. They define a wave medium'smaterial properties.

For lossless homogeneous cases (L and C constant and R(x, s)=G(x, s)=0),Eq. 12 trivially reduces to the wave equation Eq. 10 having solution Eq.11 and the propagation function indirectly specifies the wave speed asEq. 5, which says that for Eq. 10, c=1√{square root over (LC)}. Equallyimportant, the wave's characteristic impedance is given by Eq. 4. Theserelations are important because they connect the wave properties γ andZ₀ to the physical constitutive relations. As an example, for acousticwave propagation, L=ρ₀, C=γ₀P₀. The speed of sound in air is thereforec=√{square root over (γ₀P₀/ρ₀)}, which is 331 [m/s], assuming ρ₀=1.23[kgm/m₃], γ₀=c_(p)/c_(v)=1.4 and P₀=105 [Pa]. FurthermoreP±/U±=Z₀=ρ₀c=407 [MKS-Rayls].

From Eq. 9, both the characteristic impedance Z₀ and a load impedance Zare required when calculating the reflectance. This problem may besolved by replacing the inhomogeneous transmission line by its Thevenincharacteristic impedance, loaded by Z_(L)(s). In this view, thecharacteristic impedance is defined as the Thevenin source impedancelooking into a very short (infinitesimal) piece of the line. When weimpulse this system, and restrict time to very short times less than δ,(say of a few microseconds), only the waves in the region δx=cδ, canplay a role in the determination of g(δ_(t)), due to the limited timeand limited speed of sound.

For the case in hand, where Z₀(x) does not depend on frequency, then itsinverse Fourier transform is, for example,ζ(x,t)=t ₀(x)δ(t)

Z ₀(x)  (15)

We call Z₀(x) the surge impedance. It follows from Eq. 7 that in thiscase R(x, s)=0. We summarize this property by saying that thecharacteristic impedance is strictly local.

Power and wave variables: In the homogeneous case the forward andbackward wave solutions of Eq. 12 are independent, and obey Ohm's LawEq. 3.

Working in the time domain, the instantaneous intensity I (x, t), atevery location x and time t, may be expressed in terms of wave variablesI(x,t)≡p(x,t)u(x,t)=[p ⁺(x,t)+p ⁻(x,t)][u ⁺(x,t)−u ⁻(x,t)],  (16)where u is the particle velocity. Expanding this gives the totalintensity (at every time instant t and every location x) in terms ofthese wave variablesI(x,t)=p ⁺(x,t)u ⁺(x,t)−p ⁻(x,t)u ⁻(x,t)+[p ⁻(x,t)u ⁺(x,t)−p ⁺(x,t)u⁻(x,t)].  (17)

The first term on the right is denoted the forward traveling(anterograde) intensityI ⁺(x,t)=p ⁺(x,t)u ⁺(x,t),  (18)while the secondI ⁻(x,t)=p ⁻(x,t)u ⁻(x,t)  (19)is denoted the reflected (retrograde) intensity. This leaves the thirdterm in square brackets, which we denote the cross-intensityI _(c)(x,t)≡[p ⁻(x,t)u ⁺(x,t)−p ⁺(x,t)u ⁻(x,t)].  (20)

Lossless homogeneous case: Eq. 3 requires that the cross-intensity iszero, because

$\begin{matrix}{{Z_{0} \equiv \sqrt{\frac{L}{C}}} = {\frac{P^{+}}{U^{+}} = \frac{P^{-}}{U^{-}}}} & (21)\end{matrix}$is a constant. Transforming Eq. 21 to the time domain results inp_(±)=Z₀u_(±). Substitution into the cross-intensity and factoring outthe common constant Z₀ results inI _(c)(x,t)=Z ₀(x)[u ⁻(x,t)u ⁺(x,t)−u ⁺(x,t)u ⁻(x,t)]=0.  (22)

In conclusion, for the lossless homogeneous systemI(x,t)=I ⁺(x,t)−I ⁻(x,t),  (23)namely the intensity absorbed is the forward traveling intensity lessthe backward traveling intensity. This physically makes sense in thesense that the intensity either is traveling one way or the other(homogeneous property), since no energy is burned up in the network(lossless property). The cross-intensity is always zero since there isno fixed relationship between waves going in the two directions.

In the case of a lossless inhomogeneous, when L(x) and C(x) areindependent of frequency, then both the reflection coefficient R(x) andZ₀ do not depend on frequency. As for the lossless inhomogeneous case,cross-intensity must be zero since then using Eq. 9 given_(Q)(t)=R(x)δ(t), leading to, for example,I _(c)(x,t)=R(x)[p ₊(x,t)u ₊(x,t)−p ₊(x,t)u ₊(x,t)]=0.  (24)

Thus for the lossless inhomogeneous case, Eq. 23 will holds, since R(x)is a real and independent of frequency.

In the general case, when the constitutive relations depend on frequency(dispersive case), the cross-intensity is not zero, as there must belocally stored energy in the reactive terms. We deal with this case inthe frequency domain with the following proofs.

The following is a second proof, which demonstrates Eq. 23 directly.From the basic definitions

$\begin{matrix}{{I\left( {s,x} \right)} = {{\frac{1}{2}{\Re\left\lbrack {PU}^{*} \right\rbrack}} = {\frac{1}{2}{\Re\left\lbrack {\left( {P_{+} + P_{-}} \right){y_{0}\left( {P_{+} - P_{-}} \right)}^{*}} \right\rbrack}}}} & (25)\end{matrix}$resulting in Eq. 23

$\begin{matrix}{{{\frac{1}{2}\Re\; Y{P}^{2}} = {{\frac{1}{2}Y_{0}{P_{+}}^{2}} - {\frac{1}{2}Y_{0}{P_{-}}^{2}}}},} & (26)\end{matrix}$where Y is the ratio of the total volume velocity U divided by the totalpressure P_(m).

This follows because the cross term is purely imaginary, namelyP ₊ *P ⁻ −P ₊ P ⁻*=2j

P ₊ *P ⁻,  (27)thus after taking the real part we get zero.

This may be the most intuitive proof: We wish to show Eq. 23 is true, inthe frequency domain:

$\begin{matrix}{{{I(s)} \equiv {\frac{1}{2}\Re\;{PU}^{*}}} = {\frac{{P}^{2}}{2}\Re\; Y}} & (28)\end{matrix}$

Since P=P₊+P⁻=P₊(1+R) and using

${I_{+} = {{P_{+}}^{2}\frac{Y_{0}}{2}}},$

$\begin{matrix}{{I(s)} = {\frac{Y_{0}}{2}{{\left( {1 + R} \right)P_{+}}}^{2}{\Re\left( \frac{Y}{Y_{0}} \right)}}} & (29)\end{matrix}$

We need the real part of Y/Y₀ which is given by, for example,

$\begin{matrix}{{\Re\;\frac{Y}{Y_{0}}} = {{\Re\frac{1 - R}{1 + R}} = {\frac{{\Re\left( {1 - R} \right)}\left( {1 + R^{*}} \right)}{{{1 + R}}^{2}} = \frac{1 - {R}^{2}}{{{1 + R}}^{2}}}}} & (30)\end{matrix}$

Using this result in our expression for the total intensity givesequation 23 as desired.

The propagation of these waves is determined by a locally definedpropagation function Eq. 5, that also depends exclusively on theconstitutive relations. It immediately follows that intensity waves aredefined for each of these waves (Eq. 6).

For the case of homogeneous wave propagation, the waves are exclusivelycoupled at the boundaries. In the inhomogeneous case, reflections occureverywhere the impedance changes (e.g., where ε(x, s)≠0).

The exponential horn is a helpful example, since the exact closed formsolution is known. It has been shown that an approximation of the inputimpedance looking into an exponential horn can be a parallel combinationof a mass and resistive terms. The characteristic impedance Z₀(x, s) isdistinct from Z_(r)(x, s) or Z₁(x, s), which are the input impedanceslooking right and left from point x into an infinite piece of hornrespectively. Since the characteristic impedance is local, it is notdepended on direction. These are key properties of the characteristicimpedance which are used in the definition of the independent waveintensities (Eq. 6), coupled only by reflections due to inhomogeneitiesin the medium. It would be interesting to know how these definitionsgeneralize to cases of losses and dispersive constitutive relations.

Properties of q(x, t)

R(x, s): The reflectance is q(x, t) zero for t=0+ if and only if theimpedance is continuous in space, Namely R(x,t) is strictly causal onlywhen Z₀(x⁻)=Z₀(x⁺), such that the impedance Z₀(x, s) has no jumps. Whenthere is a jump, then the real part of R(s, x)≡(Z−Z₀)/(Z+Z₀) will not bezero. This can be easily seen by writing down the expression for r(t) asthe inverse Laplace transform of R(s, x), and then setting t=0 in theexpression. The imagine part of R is zero, due to the real property ofr(t), and the real part of R(s, x) gives r(t=0,x), and is zero. The realpart of a complex characteristic impedance

Z₀ is known as the surge impedance. It is zero if

Z=

Z₀ are equal, namely iff the surge impedance of Z and Z₀ are equal. Thisrequires continuity of Z₀(x, s) at x. In general, when the loadimpedance Z₀(x, s) has the surge impedance Z₀(x, s), the reflectance isstrictly causal. For example, this is easily seen by writing theexpression for the Laplace transform of g(x, t) evaluated at t=0, Theimaginary part of the integrand is then zero, due to the real property(i.e., R*(−ω)=R(ω)), where * is the symbol for conjugate, while the realpart evaluates to g(x, 0), which is zero when the surge impedance is Z₀.

The wave coupling is summarized most dramatically in terms of the wavereflectance, Eq. 9, since this goes to zero when ε(x, s)=0. In the timedomain reflectance may be expressed as a convolution p_(∓)(x, t)=q(x,t)*p_(∓)(x, t), where * indicates convolution with respect to time andq(x, t)

R(x,s) represent a Laplace transform pair. When R(x) is independent offrequency, q(x, t)=R(x)δ(t).

Because the incident pressure (P₊) and intensity (I₊) is not a functionof x, the distance placement of the receiving transducer, it's value isnot affected by the distorting effect of standing waves. Further,assuming that the power absorbed by the middle ear is negligible, theincident power intensity (I₊) is a good measurement of how much powerhas been actually delivered to the inner ear. As a result, any hearingloss measurement using the incident power intensity would be much morereliable.

Armed with measurements of the power reflectance (R) and the incidentwave pressure (P₊), one may quickly determine the hearing status of apatient. In one embodiment, The magnitude of the power reflectance value|R|, which is between 0 and 1, measured at a pure tone may be used todetect problems with the middle ear while the value of the incident wavepressure (P₊) at the same frequency may be used to detect inner earproblems. For instance, if |R| is approaching a low level of between 0.1and 0.3, it is a clear indication that the middle ear is fine becausemost of the sound has been absorbed through the middle ear. On the otherhand, if |R| is approaching a high level of between 0.8 and 0.95, it isa clear indication that there are middle ear problems because most ofthe sound energy is reflected back.

Take, as an extreme example, the case when |R| is approaching 0, itindicates that close to 100% of the sound energy has been transmittedinto the middle ear. In that case, one can safely assume that thepatient does not have any middle ear pathologies. On the other hand, if|R| is approaching 1, it indicates that close to all of the sound hasbeen reflected away from the middle ear. As a result, one may safelyconclude that the patient has problems with its middle ear.

Similarly, according to another embodiment, since the value of P₊ is aclose approximation of the sound energy that reaches the inner ear, itis a reliable indicator of inner ear problem. For instance, if themeasured threshold P₊ for a patient is much more than 20 dB-SPL for a 1kHz pure tone, then it is a clear indication that the patient suffersfrom inner ear problem.

In some embodiment, the P₊ value may be used for hearing aid fitting,reducing the variability in measurements and improving the efficiency ofthe hearing aid.

FIG. 3 is a simplified block diagram of a method for determining ahearing threshold according to an embodiment of the present invention.Merely as an example, the method depicted relates to a pure toneaudiometry (PTA) hearing test. However, the described method may easilybe adapted for use with various other types of hearing loss tests suchas OAE measurements and auditory brainstem response (ABR) measurements.

The method 300 includes a process 302 for calibrating an audiometer, aprocess 304 for selecting and generating a test tone frequency, aprocess 306 for selecting and generating a sound source volume level, aprocess 308 for determining whether a hearing threshold has beendetected, a process 310 for measuring the threshold pressure (P_(m)), aprocess 312 for determining the reflectance (R), and a process 314 fordetermining the incident wave pressure (P₊) and a process 316 fordetermining a hearing status.

At the process 302, the audiometer is being calibrated. For example, themain objective of calibration is to make sure that the audiometer ismaking consistent measurements thereby allowing abnormal results to bedistinguished from those of typical normal ears. In one embodiment, theaudiometer may be calibrated with the traditional RETSPL method. Inanother embodiment, calibration may be carried out using an impedancecavity as it is shown and described in U.S. Patent Application No.2007/0219458 entitled “Method and System for Determining HearingStatus.” In yet another embodiment of the present invention, calibrationmay be carried out in a real-ear situation using the incident pressure(P₊), the incident power intensity parameter (I₊), or absorbed intensityvalue that is determined by the process described below.

At the process 304, a test tone frequency is selected. Depending on theapplication, the frequency may be selected from a wide range offrequencies that is audible to a normal human ear, which typicallyranges from 100 Hz to 20k Hz.

At the process 306, a sound source volume level is selected anddelivered to the ear canal. At the process 308, a determination is madeof whether a hearing threshold has been detected. The two processes 306and 308 may be repeated until a hearing threshold has been detected asdescribed herein:

In one embodiment, the sound source volume level is turned down indecremental steps from a volume level that a subject can hear, like 70dB. Then, the level is turned down in large steps (for example, 20 dB)until it cannot be heard. Then the process is repeated again, startingat the last audible level, but in a smaller steps. This is repeateduntil the threshold is determined to within 5 dB.

At the process 310, the pressure (P_(m)) in the ear canal is measured.In one embodiment, the pressure is measured using a microphonepositioned at the opening end of the ear canal.

At the process 312, the power reflectance (R) of the tested ear isdetermined. In one embodiment, the power reflectance may be derived fromthe measured pressure as it is disclosed in a paper by Susan E. Voss andJont B. Allen entitled “Measurement of Acoustic Impedance andReflectance in the Human Ear Canal.” 95 J. Acoust. Soc. Am. 372 (January1994). In another embodiment, the acoustic reflectance may be measuredusing one of a plurality of reflectance measurement systems such as theRMS/MEPA3 manufactured by Mimosa Acoustics, Inc.

At the process 314, the pressure measurement in the ear canal isconverted into incident wave pressure (P₊). In one embodiment, theincident wave pressure (P₊) is also called the forward wave pressure. Inanother embodiment, the incident wave pressure (P₊) is derived from theear canal pressure measurement (P_(m)) and the ear canal reflectance (R)using the following equation:

${P_{+}(f)} = \frac{P_{m}\left( {x,f} \right)}{1 + {R\left( {x,f} \right)}}$

While the embodiment shown in FIG. 3 is adapted for use in pure toneaudiometry, the method can be easily adapted for use with various OAEmeasurements such as distortion product otoacoustic emissionmeasurements, transient otoacoustic emission measurements, and stimulusfrequency otoacoustic emission measurements.

Moreover, according to certain embodiments, at the process 316, ahearing status is determined. For example, such determination isperformed based on at least the power reflectance (R) and the incidentwave pressure (P₊). In one embodiment, the power reflectance value (R)measured at a pure tone frequency of 1k Hz may be used to detectproblems with the middle ear while the result from using incident wavepressure (P₊) at the same frequency may be used to detect inner earproblem.

For example, if R is approaching a low level (e.g., 0 for 1 kHz puretone), the middle ear is considered normal, but if R is approaching ahigh level (e.g., 1 for 1 kHz pure tone), the middle ear is consideredabnormal. In another example, if the measured threshold P₊ for a patientis much more than a threshold level (e.g., 20 dBspl for 1 k Hz puretone), the inner ear is considered abnormal.

As discussed above and further emphasized here, FIG. 3 is provided onlyas an example, which should not unduly limit the scope of the claimsherein. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, in someembodiments, the process 316 can be skipped. In another example, theprocess 314 is performed to determine the incident wave pressure, butthe incident power intensity is not determined at the process 314.

FIG. 4 is a simplified diagram illustrating a system 400 for determiningan incident wave pressure according to an embodiment of the presentinvention. The system 400 includes a probe 402, a signal generator 406,a signal processor 408, and a data processor 410. According to certainembodiments, the system 400 can be used for screening and/or diagnosinghearing disorders.

As shown in FIG. 4, the probe 402 is connected to the signal generator406 and the signal processor 408, and the signal processor 408 isconnected to the data processor 410. According to an embodiment, thesystem 400 includes a probe 402 being adapted to be placed inside a earcanal 404. The probe 402 may include a source transducer for making asound and a receiving transducer for detecting sounds. The sourcetransducer in the probe 402 is connected to a signal generator 406 whilethe receiving transducer 402 is connected to a signal processor 408. Thesignal generator 406 is responsible for delivering a signal to thesource transducer for the production of one tone, multiple tones, or asweep of continuous tones. The signal processor 406 receives signalsfrom the receiving transducer in the probe 402 and turns them intopressure measurements (P_(m)). A data processor 410 is connected to thesignal processor 408. The data processor 410 receives the pressuremeasurements (P_(m)) from the signal processor 408 and computes thevalue of a corresponding power reflectance (R). With P_(m) and R, thedata processor 410 further computes the incident wave pressure (P₊)according to the formula shown above.

According to some embodiments, the data processor 410 then computes theincident wave intensity (I₊) according to the following equation:

$I_{+} = \frac{Y^{*}{P_{m}^{2}}}{\left( {{1 + R}} \right)^{2}}$

In the embodiment of the present invention described above, the soundcould be a pure tone signal that is customarily used for hearingdiagnosis. For instance, the sound could be pure tone at 1 k Hz, afrequency that is commonly use for detecting middle ear pathologies. Inother embodiments, the sound could be multiple tones, a continuous sweep(chirp) of frequencies in the audible range, or other stimulus types.Such sounds would be ideal for performing other hearing test such asotoacoustic emission measurements and the characterization of thefrequency response of a ear canal. In yet another embodiment, the signalgenerator 406, the signal processor 408, and the data processor 410 maybe performed by a computer device configured to generate signals,receive signals, process signals, and calculate for a desirable result.

The present invention has various advantages over conventionaltechniques. Certain embodiments can provide hearing testing systems andmethods that produces results that are affected by reduced influencefrom standing waves or even free from any distortion by standing waves.Some embodiments can provide hearing testing systems and methods thatcould better distinguish inner ear hearing problems from middle earhearing problems.

Some embodiments of the present invention can significantly lower thecost of ear screening. For instance, some embodiments of the presentinvention reduce the number of false-positives in a hearing testingprograms by isolating middle ear problems from inner ear problems.

Some embodiments of the present invention provide more accuratedetermination of hearing status by isolating the incident wave pressurefrom that of measured pressure, the present invention eliminates theeffects of standing waves. As a result, the computed incident pressureis a better representation of the actual sound pressure that is beingtransmitted to the eardrum.

Some embodiments of the present invention provide significantimprovement over conventional ear screening methods by taking intoaccount of the retrograde waves. For example, some embodiments of thepresent invention derive a power measurement that reduces the effect ofthe retrograde waves on the power measurement, thereby making themeasurement more accurate.

In some embodiments of the present invention, the incident wave pressurecan be used for better hearing aid fitting.

With a more accurate measurement of the incident power to the ear drum,some embodiments of the present invention allow for a more reliablecalibration of the audiometer.

With a more accurate measurement of the sound level delivered to theinner ear, some embodiments of the present invention allow for a moreaccurate result from the pure tone audiometry, distortion productotoacoustic emission measurements, transient otoacoustic emissionmeasurements, and stimulus frequency otoacoustic emission measurements.

While many specific examples have been provided, the above descriptionis intended to illustrate rather than limit the invention. Manyvariations of the invention will become apparent to those skilled in theart upon review of this specification. The scope of the inventionshould, therefore, be determined not with reference to the abovedescription, but instead should be determined with reference to theappended claims along with their full scope of equivalents.

1. A method for characterizing an incident pressure wave in a hearingtest, the method comprising: introducing a sonic stimulus into an earcanal with a sound source transducer positioned in an ear canal;measuring at least a sound pressure level (P_(m)) in said ear canal witha receiving transducer in the ear canal; processing information, with aprocessor, associated with said sound pressure level; determining, witha processor, at least an acoustic reflectance (R) including a real andimaginary part based on information associated with said sound pressurelevel; determining, with a processor, an incident wave pressureparameter (P+) in said ear canal according to:P+=Pm/(1+R); determining based upon the incident pressure wave parameter(P+), with a processor, a voltage to apply to the sound sourcetransducer to keep an incident wave pressure (P+) approximately constantwith respect to frequency, wherein the voltage is a function offrequency in order to remove a standing wave field from the measuredsound pressure.
 2. The method of claim 1 further comprising determiningan incident wave intensity parameter from said incident wave pressureparameter (P+).
 3. The method of claim 2 further comprising performingequipment calibrations and hearing threshold measurements using saidincident wave intensity parameter.
 4. The method of claim 1, whereinsaid sonic stimulus is a pure tone.
 5. The method of claim 1, whereinsaid sonic stimulus is chirp.
 6. The method of claim 1, wherein saidsonic stimulus comprises of multiple pure tones.
 7. The method of claim3, wherein said hearing threshold measurements comprises a pure toneaudiometry.
 8. The method of claim 3, wherein said hearing measurementcomprises a distortion product otoacoustic emission measurement.
 9. Themethod of claim 3, wherein said hearing threshold measurements comprisesa transient otoacoustic emission measurement.
 10. The method of claim 3,wherein said hearing threshold measurements comprises a stimulusfrequency otoacoustic emission measurement.
 11. A method for determininga hearing threshold, the method comprising: delivering a sonic stimulusassociated with one or more frequencies and one or more volume levels toan ear canal with a source transducer positioned in an ear canal;measuring one or more sound signals (P_(m)) with a receiving transducerpositioned in the ear canal; determining, with a processor, at least anacoustic reflectance (R), including a real and imaginary part, based oninformation associated with said sound pressure level, determining, witha processor, an incident wave pressure parameter (P₊) in said ear canalaccording to:P ₊ =P _(m)/(1+R); and determining based upon the incident pressure waveparameter (P+), with the processor, a voltage to apply to the soundsource transducer to keep an incident wave pressure parameter (P₊)approximately constant with respect to frequency, wherein the voltage isa function of frequency in order to remove a standing wave field fromthe measured sound pressure; determining a threshold volume level, witha processor, for said sonic stimulus, wherein the threshold volume levelis determined based on the constant incident wave pressure parameter(P₊); measuring at least a sound pressure level of said ear canal atsaid threshold volume using said receiving transducer; processinginformation, with a processor, associated with said measured soundpressure level; determining, with a processor, an acoustic reflectancebased on at least information associated with said measured soundpressure level; and determining, with a processor, a threshold value foran incident wave pressure parameter in said ear canal based on at leastinformation associated with said measured sound pressure level and saiddetermined acoustic reflectance; wherein said threshold value for saidincident wave pressure parameter representing said hearing threshold.12. The method of claim 11 further comprising determining a hearingstatus based on at least information associated with said thresholdvalue for said incident wave pressure parameter and said acousticreflectance.
 13. The method of claim 12, wherein said process fordetermining a hearing status includes determining status of a middle earbased on at least information associated with said acoustic reflectance.14. The method of claim 12, wherein said process for determining ahearing status includes determining status of an inner ear based on atleast information associated with said threshold value for said incidentwave pressure parameter.
 15. The method of claim 11 further comprisingdetermining an incident wave intensity parameter from said incident wavepressure parameter (P+).
 16. The method of claim 15 further comprisingusing said incident wave intensity parameter for equipment calibrationand hearing threshold measurements.
 17. The method claim 11, whereinsaid process for providing a probe includes providing said probe with asource transducer and a receiving transducer, said source transducerbeing configured to deliver said sonic stimulus associated with one ormore frequencies and said one or more volumes, said receiving transducerbeing configured to measure said one or more sound signals.
 18. Themethod claim of 11, wherein said process of determining a thresholdvolume level comprises delivering a decrementally lower volume of asound signal to said ear canal until a hearing threshold has beendetected.
 19. The method of claim 11 further comprising calibrating aplurality of probe parameters, said plurality of parameters beingrelated to at least said one or more frequencies and one or more volumelevels of said sonic stimulus.
 20. The method claim 11, wherein saidsonic stimulus is a pure tone.
 21. The method of claim 11, wherein saidsonic stimulus is chirp.
 22. The method of claim 11, wherein said sonicstimulus comprises of multiple pure tones.
 23. The method of claim 11,wherein said hearing threshold measurements comprises a distortionproduct otoacoustic emission measurement.
 24. The method of claim 16,wherein said hearing threshold measurements comprises a transientotoacoustic emission measurement.
 25. The method of claim 16, whereinsaid hearing threshold measurements comprises a stimulus frequencyotoacoustic emission measurement.
 26. A system for determining anincident wave pressure in a hearing test, the system comprising: a probeadapted to be placed near an opening of a ear canal, said probecomprises a source transducer for delivering a sound and a receivingtransducer for detecting a sound; a signal generator connected to saidsource transducer, said signal generator being configured to send one ormore first electronic signals to said source transducer for deliveringsaid sound; a signal processor connected to said receiving transducer,said signal processor being configured to receive one or more secondelectronic signals from said receiving transducer and to determine atleast a sound pressure level (P_(m)) based on at least informationassociated with said one or more second electronic signals; a dataprocessor connected to said signal processor, said data processor beingconfigured to receive and process at least information associated withsaid determined sound pressure level (P_(m)) and to determine anacoustic reflectance (R); wherein said data processor is furtherconfigured to determine an incident wave pressure parameter (P₊) in saidear canal according to:P ₊ =P _(m)/(1+R) wherein said data processor is further configured todetermine based upon the incident pressure wave parameter (P+), avoltage to apply to the source transducer to keep an incident wavepressure parameter (P₊) approximately constant with respect tofrequency, wherein the voltage is a function if frequency in order toremove a standing wave field from the measured sound pressure.
 27. Thesystem of claim 26, wherein said data processor is further configured todetermine an incident wave intensity from said incident wave pressureparameter (P₊).
 28. The system of claim 26, wherein said sound is a puretone at a predetermined signal frequency in an audible range.
 29. Thesystem of claim 26, wherein said sound is a continuous sweep offrequencies within an audible range.
 30. The system of claim 26, whereinsaid sound is comprising of two tones of different frequencies within anaudible range.
 31. The system of claim 26, wherein said signalgenerator, said signal processor, and said data processor are one ormore components of a computer device.
 32. A method for characterizing anincident pressure wave in a hearing test, the method comprising:introducing a sonic stimulus into an ear canal with a sound sourcetransducer positioned in an ear canal; measuring at least a soundpressure level (P_(m)) in said ear canal with a receiving transducer inthe ear canal; processing information, with a processor, associated withsaid sound pressure level; determining, with a processor, at least anacoustic reflectance (R) including a real and imaginary part based oninformation associated with said sound pressure level; determining, witha processor, an incident wave pressure parameter (P₊) in said ear canalaccording to:P ₊ =P _(m)/(1+R); wherein said ear canal is terminated by its owncharacteristic impedance Z₀ and; determining based upon the incidentpressure wave parameter (P+), with a processor, a voltage to apply tothe sound source transducer to keep an incident wave pressure parameter(P₊) approximately constant with respect to frequency, wherein thevoltage is function of frequency in order to remove a standing wavefield from the measured sound pressure.